Quiescent memory CD4 T cells harboring integrated, actively repressed HIV proviruses currently form a formidable barrier to viral eradication. This latent reservoir could be attacked by activating proviral gene expression thereby sensitizing the virus to antiretroviral therapy . For success, this strategy must both prevent viral spread and result in the death of all latently infected cells without producing a toxic state of generalized cellular activation. Currently, no effective therapies for HIV latency exist. We hypothesize that a more complete understanding ofthe molecular underpinnings of HIV latency?notably, the full range of the host's regulatory factors that promote and antagonize latency?will facilitate the development of effective therapies. In Aim 1, we will examine five novel candidate HIV repressors identified by genome wide siRNA screening of HIV-infected HeLa cells. These candidates have biological properties consistent with a role in latency and are expressed in lymphoid tissues. Expression of these candidate genes will be analyzed in biologically relevant cells and their function assessed by lentiviral shRNA knockdown. In Aim 2, we will screen a CD4 T-cell model of HIV latency for microRNAs (miRs) that promote viral latency by impairing the expression of cellular activators. We will validate mlR action using antagomirs in latently infected primary CD4 T-cells. In Aim 3, we will use bioinformatics and transcriptional profiling approaches to identify the host gene products that are suppressed by these miRs. Using this dual experimental approach, we will identify cellular factors that naturally promote and antagonize HIV latency. Where appropriate, mechanism-of-action studies will be performed. Identified targets will be prioritized, based on the robustness of their activity and overall drugability, for entry into small-molecule high-throughput screening assays and primary and secondary screening assays will be developed. These proposed studies could identify small molecules that either inhibit the most interesfing cellular repressors or activate the most compelling mlRNAregulated HIV activators. These studies fully support the goal of the Collaboratory?to identify combinafions of nontoxic small molecules that can eradicate the virus or produce a funcfional cure (drug-free remission).